it's not over rated, a REALLY GOOD GP can 1 v 9 in the late game, here is the problem with the concept of late game play styles.
My advice? Don't make that your style.
Good players will tell you this piece of advice and spam it in your ear. "End the game as quickly as possible the moment you can"
Many good streamers will say "that games was 5 minutes longer than it should of been" And they will say it with bitterness.
Why?
For the moment late game happens, for the most part the game is NO LONGER in your control. Death timers become 60 seconds, and typically the team with the better draft will win. All it takes for you to lose late game, is for a single teamate to get caught out and die. The moment this happens the enemy team if they are smart will run it down mid, take your towers, and rush to take your nexus. Why? Because they have more people, they a clear and obviously mathmatical advantage.
You lose SO MUCH control over the flow of the game once late game happens, it sounds like a exaggeration but a single players fuck up can actually cost you the game, and their is not to much you can do to stop it. If you have a lead, end the game as quick as possible to prevent this from happening, because once everyone has 6 items, your lead no longer matters. Your mechanics and shot calling will only get you so far.
Players like Box Box win games, because he will dumpster people in lane phase, and abuse his lead as harshly as possible and quickly as possible.
TLDR-late game = hell, even for late game champions.